The present invention relates generally to fluid infusion systems, and more particularly to an improved apparatus for detecting the formation of bubbles in such systems.
The infusing of fluids such as parenteral fluids and blood into the human body is usually accomplished by means of an administration set and metering apparatus which controls the rate of flow of fluid through the set. Peristaltic-type pumps, which function by repetitively compressing and expanding a section of tubing, have proven particularly attractive for use in such metering apparatus since they do not introduce the possibility of leakage or contamination into the system, while providing positive control of fluid flow through the system. One form of metering apparatus employing a peristaltic-type pump is described in U.S. Pat. No. 4,155,362, which issued to Thurman S. Jess on May 21, 1979, and is assigned to the present assignee. A successful commercial embodiment of this apparatus is currently marketed as the Travenol Model 2M014 infusion pump by Baxter Travenol Laboratories, Inc., of Deerfield, Illinois.
One problem which arises with the use of liquid infusion sets is that dissolved gases in the liquid being infused may be released as bubbles as the liquid is subjected to pressure and/or temperature changes as it passes through the pump of the metering apparatus. These bubbles may coalesce and form larger bubbles or pockets of gas which may be infused along with the liquid into the body, an occurence which may be harmful or even fatal to the patient under certain circumstances.
To prevent gas from being infused it has become common practice to locate a bubble detector downline of the metering apparatus pump to automatically stop the apparatus should gas bubbles be detected. Such sensors typically employ a light source and a light detector positioned on opposite sides of the administration set tubing to monitor the level of light transmitted through the tubing. Operation of the metering apparatus is interrupted and an alarm is sounded when the transmitted light level falls below a predetermined level. To this end, the lens effect of the fluid in the lumen of the tubing may be employed to enhance the difference in transmission levels between fluid and no fluid conditions.
One problem encountered with such bubble detectors is that fluid pressure changes in the tubing of the administration set such as may result from the use of a downline flow restriction, as in the Travenol Model 2M8014 infusion pump may deform the wall of the tubing from its unstressed shape and diminish the lens effect. This has the potential of diminishing the reliability and sensitivity of the bubble detector. The present invention is directed to a bubble detector which is not subject to such variations in effectiveness as a result of changes in fluid pressure.
Accordingly, it is a general object of the present invention to provide a new and improved bubble detector.
It is another object of the present invention to provide a new and improved bubble detector wherein means are provided for preventing deformation of the tubing wall as a result of internal fluid pressure.
It is a further object of the present invention to provide a new and improved bubble detector suitable for use with vinyl tubing or the like subject to deformation from internal fluid pressure.